Base: Fix floating point issue in schema threshold comparison

When a parsed value lands exactly at a threshold boundary (e.g. "1 S/m"
= 1e-9 at threshold 1e-9), floating point rounding could cause the
wrong unit to be selected. Shrink thresholds by a relative epsilon so
boundary values fall through to the next (more natural) unit.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

src/Base/UnitsSchema.cpp

@@ -67,7 +67,11 @@ std::string UnitsSchema::translate(const Quantity& quant, double& factor, std::s
 
     const auto value = quant.getValue();
     auto isSuitable = [&](const UnitTranslationSpec& row) {
-        return row.threshold > value || row.threshold == 0;  // zero indicates default
+        // Shrink threshold slightly so values at exact threshold boundaries
+        // (e.g. "1 S/m" = 1e-9 at threshold 1e-9) fall through to the next unit.
+        constexpr double relEps = 1e-12;
+        return row.threshold * (1.0 - relEps) > value
+            || row.threshold == 0;  // zero indicates default
     };
 
     auto unitSpecs = spec.translationSpecs.at(unitName);